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Battery issue - not parasitic drain?

Matthewjw

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Hi guys.
This one has me a little stumped.

I have a 2000 vt and am working on a 98 vt project.

The project is having a battery issue. Starts when charged but drains after 24-48 hours.

So I thought parasitic drain. However test shows about 95 milliamps. Same test on 2000 vt shows about 130 milliamps (and it has no battery issue) - so assume okay.

Tried a couple of batteries (known good) and it does same thing.

Tested all fuses and did replace 2.

The car is not being driven but sucks the volts from 12.8+ down to 4v in record time after battery attached.

Assume a bad alternator would have to have the vehicle started to be as issue.

Not sure what else could impact battery in such a way? If the fuses were an issue, then the fact they had blown should have cut the circuit.

Other shorts would show up in parasitic drain test?

Any ideas?
 

lout

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faulty battery
is car going into battery saver (after 2 hours)
 

Matthewjw

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Tried two batteries known to be good.

Not getting battery saver mode message.
 

lout

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Not getting battery saver mode message.
the vt-vx has a battery saver mode, after 2 hours of key off, from memory, extra circuitry is disabled to prevent flat batteries, from memory glove box light, boot light, interior light and not sure what else
a bad alternator will discharge battery if it has a shorted rectifier whether engine is running or not
 

Matthewjw

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I thought the alternator might be next area to consider. Any easy way to test? The battery is hitting 14v when engine running so I thought that looked okay....
 

lout

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simply remove all wiring to alternator and insulate them
 

Schtoo

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When you do the drain test, how are you doing it and with what? Sounds perfectly reasonable if the figures you gave are true and accurate and especially if that's within a few minutes of shutting it down.

What I'd be doing next is checking whether the alternator is actually pushing something meaningful into the battery (because a surface charge will make a depleted battery look great, for a time) and yes, as mentioned, whether something else is sucking the battery dry like a bad alternator.

Also make sure your earths are in good shape, one of the 'trick' things good auto-elecs check which solves a lot of problems right quick and keeps them in steak and beer. ;)

If you've got a decent battery charger, get the battery tested on a carbon pile tester as well after it's been fully charged, or as close to it as you can manage. Electronic testers have their value, but the pile takes no prisoners as it either passes or it doesn't and watch the dials during the test. You're looking for the battery to be able to push out it's rated CCA or a solid fraction it while holding voltage at or above 10v. The tester will have the dials marked suitably and someone who knows how to drive one will get an accurate result from a sad battery without completely killing it.

I have sluggish starting, mostly iffy earths (which are semi-cured) and a sad starter, but the battery is in great shape, which sucks because batteries are dirt cheap (for me) and easy to change, but the rest of the mess isn't. But it'll all be solved this time tomorrow come whatever. :)
 

Matthewjw

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Thank you lout. Dodgy alternator or voltage regulator. I think ill just replace both.
 

lout

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just replace rectifier assembly unless alternator is very noisy as well
 
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